KVM: PPC: Book3S HV P9: Demand fault EBB facility registers

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Use HFSCR facility disabling to implement demand faulting for EBB, with
a hysteresis counter similar to the load_fp etc counters in context
switching that implement the equivalent demand faulting for userspace
facilities.

This speeds up guest entry/exit by avoiding the register save/restore
when a guest is not frequently using them. When a guest does use them
often, there will be some additional demand fault overhead, but these
are not commonly used facilities.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-37-npiggin@gmail.com

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Nicholas Piggin 2021-11-23 19:52:14 +10:00 • committed by Michael Ellerman

parent 34e02d555d

commit a3e18ca8ab

3 changed files with 37 additions and 8 deletions

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1

arch/powerpc/include/asm/kvm_host.h

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16

arch/powerpc/kvm/book3s_hv.c

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28

arch/powerpc/kvm/book3s_hv_p9_entry.c

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